A de-emphasis of a signal can be generally defined as reducing a signal level, such as a voltage level, of all bits except the first one after a transition from a value of one to a value of zero in a differential signal, and vice versa. This, in turn, causes a high frequency content of the signal, due to the de-emphasis transition, to be emphasized, when compared to the low frequency content, which is de-emphasized. This is one form of transmitter equalization between high frequencies and low frequencies. This form of transmitter equalization compensates for losses over a transmission channel, which is typically higher at higher frequencies.
A universal serial bus (USB) 3.0 normative LFPS Electrical Specification Table 6-20 calls for a USB 3.0 transmitter or re-transmitter de-emphasis to be applied only to a High Speed 8 bit-10 bit encoded Data Communication Signal (in the “Universal Serial Bus 3.0 Specification”, a particular type of this form of signal is referred to as a “SuperSpeed” signal; SuperSpeed will henceforth be discussed, but the principles of the present application can be applied to other communication signals such as High Speed 8 bit-10 bit encoded Data Communication Signals as well) when conveying a USB 3.0 signal, but not to a low frequency periodic signal (LFPS). The USB 3.0 signal will therefore undergo a higher attenuation than a low frequency signal, and to not apply de-emphasis to the LFPS.
However, unlike a host or device in a universal serial bus (USB) 3.0 link, an USB 3.0 re-driver, a type of signal conditioner, is situated in a middle between a transmitter USB connector and a receiver USB connector, and the re-driver should be neither a source nor a sink of a USB 3.0 signal. A conventional re-driver should be transparent to both high frequency periodic signals (such as SuperSpeed) and low frequency periodic signals (LFPS).
However, use of both LFPS and HFS, such as SuperSpeed, in the same re-driver can cause serious issues regarding treatment of their differing signal characteristics between LFPS and SuperSpeed. Some conventional re-drivers disable de-emphasis completely in order to pass USB 3.0 LFPS compliance limits. However, this has a limitation that, for long channels where de-emphasis is needed, USB 3.0 signal integrity is compromised, which results in a high bit error, making the USB 3.0 connection/re-driver/link unusable.
Therefore, there is a need in the art to address at least some of the issues associated with SuperSpeed and LFPS sharing same signal path in re-drivers.